This invention relates to an apparatus used to detect the presence of a target gas in a person""s body and, more particularly, to a sensor and sensor assembly capable detecting the presence of a target gas, e.g., acetone, in a person""s body by non-invasive method of breath collection and sampling.
Chemical metabolites present within or emitted from a person""s body can serves as an important indicator or biomarker of the person""s physical or medical condition. Table 1 below sets forth a list of metabolites that are commonly found in a person""s breath, and the respective diagnostic condition of the person providing such metabolite.
Accordingly, there are a number of medical conditions that can be monitored by detecting and/or measuring a person""s breath metabolites. For example, the method of measuring a person""s breath metabolites has widely been used by law enforcement officials for the purpose of detecting alcohol intoxication of drivers and enforcing state vehicle codes relating to driving while under the influence of alcohol. In this example, the breath metabolite of interest is a ketone, e.g., acetaldehyde.
There are many types of instruments that are currently used to detect these types of ketones such as spectroscopy, GSMS and HPLC. In addition, there are three types of low-cost detectors that can be used; namely, electrochemical, chemioptical, and semiconductor. The electrochemical cell is fairly accurate detector at levels above about 10 ppm, but is not accurate at levels below about 1 ppm. Additionally, the accuracy of readings provided by such detectors can be affected by alcohol and many other vapors, making them unsuitable for general medical use.
A tin oxide sensor known as the xe2x80x9cTaguchixe2x80x9d sensor is a low-cost semiconductor sensor that is disclosed, e.g., in U.S. Pat. No. 3,676,820. However, the Taguchi sensor is known to exhibit a large sensitivity to humidity, and lacks sensitivity below 10 ppm. Therefore, making this sensor impractical for use as a breath metabolite sensor.
Thus, although breath metabolites are useful for providing a diagnostic condition of a person, the above-identified instruments and detectors known in the art are either not well suited, or do not provide a low-cost method, for providing the accurate detection or measurement of the same.
It is, therefore, desirable that a sensor and/or sensor assembly be constructed that is capable of accurately detecting and/or measuring via non-invasive method the presence of metabolites in a person""s breath in low concentrations, and under humid operating conditions. It is further desired that sensors and/or sensor assemblies of this invention provide a relatively low-cost means of rapidly diagnosing the condition of a person, e.g., infants, ill and even unconscious patients.
Sensor and sensor assemblies, constructed according to principles of this invention, provide an economical and light-weight apparatus for determining the presence of, and measuring the level of, a target gas in a collected breath sample, thereby providing a practical means for diagnosing the condition of a person. The sensor assembly generally comprises a sensor body having a chamber disposed therein for accommodating a sensor reagent or material. The chamber is defined within the body between optically transparent body portions. The chamber is in gas flow communication with a passage used for passing a collected breath to the sensor material.
In one invention embodiment, the chamber is disposed radially within a wall section of a substantially tubular body, and is interposed between optically transparent body ends. This invention embodiment is useful for accommodating a liquid sensor material. In another invention embodiment, the chamber is disposed axially through the body and the sensor material is in the form of a solid film layer disposed along an inside diameter wall surface of the chamber. The ends of the body are open and, thereby, optically transparent.
The sensor material can be in the form of a liquid or solid under operating conditions, depending on particular sensor application. In either case, the sensor material is designed to produce a change in optical properties upon exposure to a target gas within the collected breath sample by reaction therewith.
In an example embodiment, the sensor material comprises one or more ingredient selected from the groups consisting of: Group 1: sodium hydroxide, potassium hydroxide, sodium carbonate, and mixtures thereof; Group 2: alcohols, dimethyl sulfoxide, tetrahydrofuran, dimethyl formamide, chloroform, and mixtures thereof; and Group 3: salicylaldehyde and its derivatives, vanilla and its derivatives, benzaldehyde and its derivatives, and mixtures thereof. Optionally, the sensor material can also include one or more ingredient selected from Group 4 consisting of molecules of the cyclodextrin family, crown ethers, and mixtures thereof. The exact chemical ingredients used will depend on the particular application and type of target gas being detected.
In the case that the sensor material is a liquid, a gas permeable membrane can be disposed over the chamber opening to both retain the liquid sensor material therein, and to permit the diffusion of gas from the collected breath sample to the sensor material.
The sensor assembly is used with a photon source that emits photons, within a selected wavelength band, onto the chamber and sensor material, and a photon collector that is used to receive photons that exit the chamber. The photon source and photon collector can be part of the sensor assembly or can be part of a breath diagnostic assembly, of which the sensor assembly is a removable member.
An optical reading means can be used to determine the change or rate of change in the optical properties, e.g., photon adsorption, of the sensor material after it is exposed to the collected breath sample. The measured change in optical properties can then be used with other gathered information, such as carbon dioxide level, to determine the level of target gas within the collected breath sample.
Sensors and sensor assemblies of this invention can, e.g., be used to non-invasively detect of the presence and level of acetone in a collected human breath sample, which can replace current invasive procedures that can be traumatic to patients, and providing more rapid, accurate and widespread information to the medical and health professionals as well as for patients.